This collaborative project is focused on elucidation of the role of bicarbonate (BC) in the functional/structural organization of the water oxidase (WOC). Prior joint studies arising from our collaboration has shown that BC is a key component needed for assembly of the inorganic core of the WOC, particularly the binding and photo-oxidation of Mn 2+ ions. BC also has potential significance for understanding the origin of biogenesis of the inorganic core during evolution of the first 02 producing photosynthetic organisms. To investigate the possibility of direct interaction (ligation) of BC to the (Mn4Ca1Clx) core of the WOC, the EPR, ENDOR, ESE-ENDOR and FT-lR characteristics of the core will be investigated after replacement of BC for 12 C- and 13C-formate, 13C- bicarbonate and borate during reconstitution of the WOC from apo-WOC preparations and the inorganic cofactors. A possible role for BC in "switching" between the four-electron (with production of 02) to the two-electron (with production of H202) mechanism of water oxidation, will be investigated using the luminol-peroxidase assay (the sensitivity of which has been considerably increased in the Russian group). A possible role for BC in the catalase activity of the WOC will also be examined. Electrochemistry of manganese complexes with BC and other weak anions, and their capabilities to donate electrons to the WOC and to catalyse the decomposition of hydrogen peroxide will be studied to understand the specificity of the bicarbonate effect on the WOC. The health of all aerobic organisms, including man, depends upon these processes, since water oxidation is the dominant renewable source of atmospheric oxygen, while catalase protects against oxidative damage caused by hydrogen peroxide, a potent biological toxin. The specific aims of this project are directly related to the aims of the parent NIH project "Catalases and photosynthetic water oxidase." The research will be mainly done in Russia as an extension of NIH grant #5R01GM39932-1O